No abstract

Solid-state 31P-NMR of Nephila clavipes dragline silk indicates the presence of phosphorus in at least two chemically distinct environments. Amino acid analyses of acid-hydrolyzed silk confirm the presence of phosphotyrosine as one of the phosphorus-containing components. The unusual chemical shift (18.9 ppm downfield from 85% H3PO4), proton chemical shift, and acid lability of a second component suggest that it is part of a strained five-membered cyclic phosphate that might be found on a beta-D-ribose. The five-membered cyclic phosphate is not removed from the silk fibers by exhaustive aqueous extraction. It is absent in nascent silk fibroin from the glands, suggesting that its formation is part of the fiber processing that occurs in the ducts leading to the spinnerets. High-resolution NMR spectra of silk dissolved in propionic acid/12 N HCl (50:50 v/v) show five phosphorus sites assigned to phosphorylated tyrosine residues, phosphorylated serine residues, inorganic phosphate, and two hydrolysis products of the cyclic phosphate compound. The observed posttranslational phosphorylation may be important in the processing and modulation of the physical properties of dragline silk.

The phosgene-free synthesis of fast curing (2-oxo-1,3-dioxolan-4-yl)methyl acrylate (propylene carbonate acrylate, PCA) is presented. Polymerization of PCA in the presence of plasticizing propylene carbonate (PC) results in the formation of reversibly swellable elastomeric gels. The ionic conductivity of poly(PCA) plasticized with 50 wt % PC and containing 1 M lithium triflate is 1.7 x 10-5 S/cm. Evidence for Li4"-cyclic carbonate interaction was found in 13C CP-MAS NMR spectroscopic analysis of the model compound poly(vinylene carbonate) containing 1 M lithium triflate.

Results are reported for measurements of the diffusion coefficients of poly(ethy1ene oxide) fractions in aqueous solution and of the viscosities and sedimentation coefficients at temperatures between 8 and 35"C, for molecular weights from 1000 to 6000. These show that the polymers behave in water as non-free-draining coiled molecules having dimensions which become less perturbed by the solvent as the temperature is lowered, the &temperature is estimated at 5°C. The unperturbed dimensions are seen to decrease with increasing temperature due possibly to greater freedom of rotation of the atoms around the bonds joining them. The entropy parameter, $, is about 0.36, coming within the range of geometrically good solvents.